A sizing composition operable to impart desired properties is typically applied to glass fibers subsequent to glass fiber formation. As used herein, the terms “sizing composition,” “sizing,” “binder composition,” “binder,” or “size” refer to a coating composition applied to filaments after forming and include, for example, primary sizings, secondary sizings, secondary coating compositions and other coating compositions. In some embodiments, a sizing composition is applied to filaments immediately after forming or during downstream processing. Sizing compositions may provide protection to glass filaments through subsequent processing steps.
In addition, sizing compositions can play a dual role when placed on fibers that reinforce polymeric matrices in the production of composites and other products. In some applications, a sizing composition can provide fiber protection while also providing compatibility between the fiber and the matrix polymer. For example, glass fibers in the form of woven and nonwoven fabrics, mats, rovings or chopped strands have been used to reinforce thermoplastic and thermoset resins.
Depending on the mechanical and chemical properties of a polymeric material, however, compounding glass fibers with the polymeric material can require significant amounts of time and energy. Difficulties and inefficiencies encountered in compounding can limit the amount of glass fiber incorporated into a polymeric material as well as the size of the resulting composite. Thermoplastic materials, for example, often have high viscosities requiring protracted periods to achieve acceptable impregnation of glass fiber reinforcements. Moreover, in some cases, the viscosities of a thermoplastic material can preclude complete wet out of glass fiber reinforcements and produce broken glass filaments and/or strands, thereby compromising the mechanical properties of the resulting thermoplastic composite.
In view of the inefficiencies and difficulties encountered in compounding thermoplastic materials with glass fiber reinforcements, reactive processing techniques have been developed wherein thermoplastic polymeric precursors, such as monomers, are applied to glass fibers and subsequently polymerized in a mold or during pultrusion or extrusion to yield a glass fiber reinforced thermoplastic composite. Forming a thermoplastic polymeric material in the presence of glass fibers by reactive processing techniques can avoid some of the problems associated with compounding where the thermoplastic polymeric material is formed prior to combination with the glass fibers.
Nevertheless, several disadvantages exist with thermoplastic reactive processing techniques. One disadvantage is that such techniques are not available for all thermoplastic systems. Additionally, reactive processing techniques do not solve all problems with thermoplastic viscosities. Thermoplastic gellation and other increases in polymer viscosity during reactive processing can still limit acceptable glass fiber reinforcement impregnation.
Furthermore, reactive processing techniques are very sensitive to the introduction of chemical species foreign to polymerization processes. Various components of sizing compositions applied to the reinforcing glass fibers, for example, can disrupt and/or terminate a polymerization process of a reactive processing technique. Disruption or premature termination of polymerization can produce reinforced composites with undesirable mechanical and chemical properties.
As a result, sizing compositions applied to glass fibers for protection during mechanical processing are removed from glass fiber surfaces, often by the application of heat, prior to use of the glass fibers in a reactive processing technique. Removal of the sizing composition precludes the presence of disruptive chemical species during reactive processing techniques. Heating the glass fibers to remove the sizing composition, however, mechanically weakens the glass fibers thereby precluding further processing of the fibers into various reinforcement geometries. As a result, current reactive processing techniques are limited to glass fiber reinforcements in fabric arrangements. Limitation to fabric arrangements of glass fiber reinforcements excludes application of reactive processing to other composite forming techniques such as filament winding, pultrusion, extrusion and braiding.
Furthermore, heat cleaning glass fibers can negatively impact the properties of the resulting reinforced polymeric composite. As a result of these disadvantages, the commercial production of such glass fiber reinforced thermoplastic composites has been limited.